Magnetic control circuit separation slit

ABSTRACT

An electric alternator/motor having a stator with at least two non-overlapping sectors is provided. Each sector includes a first winding, first and second magnetic circuits and a saturation control assembly. A cross-talk reduction feature, such as a peripheral slit is provided between each sector of the stator for impeding magnetic flux crossing between the sectors.

TECHNICAL FIELD

The invention relates to electric machines capable of operating at leastas alternators, and in particular to the control of machines having amulti-channel design.

BACKGROUND

Electric machines can be provided with a multi-channel design. Thismulti-channel design permits a plurality of motor/alternators to existwithin the same stator, and which may either be operated conjunctively,or preferably independently if of the general type described inapplicant's U.S. Pat. No. 6,965,183, as desired. For example, in normalmachine operation as a generator, the outputs of the winding sets may becombined to provide a single output, but in the event of a fault whichrequires one winding set (i.e. one generator channel) to be shut down,the remaining winding set(s) may continue operation unaffected. Thisfeature thus permits more than one motor/generator to exist within thesame machine, thereby providing redundancy which may very valuable inapplications where a complete shutdown would be highly undesirable.

It is still desirable to improve the controllability and effectivenessof such electric machines, generally, and in particular permanent magnet(PM) machines having an independent multi-channel architecture.

SUMMARY

In one aspect, the present invention provides an electricalternator/motor comprising: a rotor having a plurality of permanentmagnets; a stator having at least two non-overlapping sectors, eachsector having a plurality of first slots and a plurality of secondslots, the first slots being located on a periphery of the statoropposing the rotor, the second slots being located on an opposite sideof the first slots relative to the rotor, at least a first windingdisposed in a plurality of said first and second slots, at least a firstmagnetic circuit which encircles at least one first slot in which aportion the first winding is disposed, at least a second magneticcircuit encircling at least one of the second slots in which anotherportion of the first winding is disposed, the second magnetic circuitremote from the first magnetic circuit, at least a second windingdisposed adjacent to the first winding in the plurality of second slots,a third magnetic circuit defined in the stator, the third magneticcircuit operatively associated with current passing through the secondwinding, and a current source connected to the second winding andadapted to pass current through the second winding to thereby causemagnetic flux to circulate third magnetic circuit; and at least one slitbetween each sector of the stator adjacent to the respective thirdmagnetic circuits, each slit separating the third magnetic circuits ofadjacent sectors and thereby adapted to impede magnetic flux crossingbetween the third magnetic circuit of each sector.

In another aspect, the invention provides a machine operable as at leastone of an electric alternator/generator and an electric motor, themachine comprising a rotor and stator assembly, the assembly having astator with at least two non-overlapping sectors, each sector includingat least a first winding, first and second magnetic circuits and asaturation control assembly, the first magnetic circuit including therotor and encircling at least a first portion of the first winding, thesecond magnetic circuit encircling at least a second portion of thefirst winding remote from the first magnetic circuit, the first andsecond magnetic circuits coupled when current flows in the firstwinding, the saturation control assembly of each sector beingoperatively associated with the corresponding second circuit andoperable to controllably vary a saturation level of a portion of itsassociated second magnetic circuit, the saturation control assemblyhaving a third magnetic circuit associated therewith which travels alonga periphery of the stator, the respective the third magnetic circuits ofthe sectors being electromagnetically separated by at least one slit insaid periphery of the stator.

In another aspect, the invention provides method of regulating anelectrical output connected to a load, the method involving at least onealternator connected to the load, the alternator having a magneticrotor, a stator having at least two non-overlapping sectors, each sectorcomprising a stator winding assembly confined to its respective sector,the stator winding assembly of each sector connected in parallel to saidload, each winding associated with at least one magnetic circuit definedin the stator sector and traveling along a periphery of the statorsector, the method comprising the steps of: providing electromagneticseparation between the sectors to electromagnetic separate theperipheral portions of the respective magnetic circuits; and moving therotor relative to the stator to generate an output current in thewindings of the sectors.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding and to show more clearly how it may becarried into effect, reference will now be made by way of example to theaccompanying figures, in which:

FIGS. 1 a to 1 c are a schematic views of an example of a single channelalternator/motor machine;

FIGS. 2 a and 2 b are a schematic views of an improved multi-channelelectric alternator/motor machine;

FIG. 3 is a schematic view of a partial equivalent circuit of thealternator/motor machine of FIG. 1, illustrating its functional aspects;

FIG. 4 is a block diagram illustrating the functional aspect of thealternator/motor machine of FIG. 2 a; and

FIG. 5 is an exploded perspective view of the windings and the stator ofthe dual-channel electric alternator of FIG. 2 a.

DETAILED DESCRIPTION

Referring first to FIGS. 2 a and 2 b, there is shown an example of aportion of a permanent magnet (PM) electric machine 10 as improvedherein. For ease of illustration and description, FIG. 2 b schematicallyshows a partial linear arrangement of the electric machine 10 of FIG. 2a. It will also be understood by the skilled reader that in FIGS. 2 aand 2 b, many routine details of the design have been omitted forclarity. The machine 10 may be configured as an alternator to generateelectrical power, a motor to convert electrical power into mechanicaltorque, or both. The following paragraphs are directed to an electricmachine operable as an alternator, but apply to a motor construction, aswell.

In order that the dual channel machine of FIGS. 2 a and 2 b may be moreeasily understood, a simpler single-channel design of FIGS. 1 a to 1 cwill first be described here. The machine 10 of FIGS. 1 a to 1 c has arotor 12 with permanent magnets 14 interposed between yokes 16, whichrotor 12 is mounted for rotation relative to a stator 20. A retentionsleeve 18 is provided to hold the permanent magnets 14 and the yokes 16.It also provides a magnetic path behind the magnets 14. Stator 20 has atleast one power winding 22 and preferably at least one control winding24. In the illustrated embodiment, the stator 20 has a 3-phase designwith three independent power windings 22 (the phases are denoted by thecircled numerals 1, 2, 3, respectively in FIG. 1 b) and,correspondingly, three control windings 24. The power windings 22 andcontrol windings 24 are separated in this embodiment by a winding airgap 26 and are disposed in radial slot portions 28 a, 28 b of slots 28provided in the stator 20 between adjacent teeth 30. For ease ofillustration in FIGS. 1 a and 1 b, the adjacent elements of the controlwindings 24 are shown unconnected. Also, the adjacent slot portions 28a, 28 b are indicated as A, B, C, etc. The first slot portions 28 a areused for the power windings 22 only, and the second slot portions 28 bare for both the power windings 22 and the control windings 24.

The power windings 22 are electrically insulated from the controlwindings 24. The insulation is provided, for instance, by a sheathing ora layer of insulation varnish or the like.

A back iron 32, also referred to as the control flux bus 32 in thisapplication, extends between and at the bottom of the second slotportions 28 b. A rotor air gap 34 separates rotor 12 and stator 20 in atypical fashion. A core or “bridge” portion, also referred to as the“power flux bus” 36 portion of stator 20 extends between adjacent pairsof teeth 30 to form the two distinct slot portions 28 a, 28 b. Powerflux bus 36 divides the spare between adjacent teeth 30 to form thefirst slot portions 28 a and the second slot portions 28 b.

The materials for the PM machine 10 may be any one deemed suitable bythe designer. Materials preferred by the inventor are samarium cobaltpermanent magnets, copper power and control windings, a suitablesaturable electromagnetic material for the stator teeth, such aselectrical silicon steels commonly used in the construction of magneticmachines. The stator teeth, power and control flux busses may beintegral or non-integral with one another, as desired.

FIG. 1 c shows an example of one of the power windings 22, positioned asit would be wound in the stator 20 in a three-phase configuration. Eachof the power windings 22 in this embodiment consists of a singleconductor which enters, for instance, the first slot portion 28 a of aselected slot 28 (e.g. at slot “A” of FIG. 1 b), extends through theslot and exits the opposite end of the slot, and then radially crossesthe power flux bus 36 to enter the second slot portion 28 b of the sameslot 28 (e.g. at slot “A” of FIG. 1 b), after which it extends backthrough the length of the selected slot, to exit the second slot portion28 b, and hence exits the slot 28 on the same axial side of the statoras it entered. The conductor of power winding 22 then proceeds to thesecond slot portion 28 b of the next selected slot 28 (e.g. slot “D” inFIG. 1 b), where the power winding 22 then enters and passes along theslot 28, exits and radially crosses the power flux bus 36, and thenenters the adjacent first slot portion 28 a of the selected slot 28, andthen travels through the slot again to exit slot portion 28 a and thestator adjacent where the winding entered the second slot portion 28 bof the selected slot 28. The power winding then proceeds to the nextselected slot 28 (e.g. slot “G” in FIG. 1 b), and so the patternrepeats. A second power winding 22 corresponding to phase 2 (not shown),begins in an appropriate selected slot (e.g. slot B of FIG. 1 b) andfollow an analogous path, but is preferably wound in an opposite windingdirection relative to winding 22 of phase 1. That is, the phase 2winding 22 would enter the selected slot (slot B) via second slotportion 28 b (since phase 1 winding 22 entered slot A via first slotportion 28 a, above), and then follows a similar but opposite path tothe conductor of phase 1, from slot to slot (e.g. slots B, E, etc.).Similarly, the phase 3 winding 22 is preferably oppositely-woundrelative to phase 2, and thus enters the selected slot (e.g. slot “C”)of the stator via first slot portion 28 a, and follows the same generalpattern as phase 1, but opposite to the pattern of phase 2, from slot toslot (e.g. slots C, F, etc.). Thus, as mentioned, the phases of thepower winding 22 are oppositely-wound relative to one another, forreasons described further below.

Meanwhile, a control winding(s) 24 is wrapped around the control fluxbus 32, in a manner as will now be described. In this embodiment,control winding 24 preferably forms loops wrapped preferably multipletimes around the control flux bus 32, such as 25 times to provide a 25:1control-to-power winding turns ratio, for reasons described below. Thedirection of winding between adjacent second slot portions 28 b ispreferably the same from slot to slot, and thus alternatingly oppositerelative to the power winding 22 of a same phase wound as describedabove, so that a substantially net-zero voltage is induced in eachcontrol winding 24, as will also be described further below. Preferably,all loops around the control flux bus 32 are in the same direction. Notethat the control winding 24 does not necessarily need to be segregatedinto phases along with the power windings, but rather may simply proceedadjacently from slot to slot (e.g. slots A, B, C, D, etc.). Alternately,though not segregated into phase correspondence with power windings 22,it may be desirable to provide multiple control windings, for example,to reduce inductance and thereby improve response time in certainsituations. Preferably, several control windings 24 are provided in aseries-parallel arrangement, meaning the control windings 24 of severalslots are connected in series, and several such windings are thenconnected in parallel to provide the complete control winding assemblyfor the machine. Although it is preferred to alternate winding directionof the power windings, and not alternate direction of the controlwindings, the power and control windings are preferably wound inrelative opposite directions and in equal slot numbers to ensure asubstantially net-zero voltage is induced in each control winding 24 asa result of current flow in the power windings 22, so that the functiondescribed below is achieved. The control winding(s) 24 is(are) connectedto a current source 50 (see FIG. 3), which in this example includes avariable current DC source and an appropriate solid state control systempreferably having functionality as described further below. If there ismore than one control winding 24, each control winding 24 can beconnected to the same current source 50, or connected to a respectiveone. The approximate current required from such source is definedprimarily by the power winding output current required and the turnsratio the power and control windings, as will be understood by theskilled reader in light of this disclosure.

Referring still to FIG. 3, each phase of the machine 10 can berepresented by an approximately equivalent circuit 10′ having aplurality of alternating current sources 12′ (i.e. each, equivalent tothe moving magnetic rotor system in conjunction with the portion of apower winding 22 located in the first slot portion 28 a) connected to aplurality of power inductors 22′ (i.e. equivalent to the portion of theprimary winding 22 located in the second slot portion 28 b), the currentsources 12′ and power inductors 22′ arranged alternately in series.Associated with power inductors 22′ are a plurality of control inductors24′ (i.e. equivalent to control winding 24) having saturable cores(equivalent to the saturable control flux bus 32). Control inductors 24′are connected to a variable DC current source and control system in thisexample, represented by 50. Therefore, one can see that the powerwinding(s) 22, the control winding(s) 24 and the control flux bus 32co-operate to provide a saturable core inductor within the stator 20.The saturable core inductor, in conjunction with other electromagneticeffects, described further below, provides an integrated approach toimplementing the power regulation schemes described below.

Referring again to FIG. 1 b, when the machine 10 is used in analternator mode, rotor 12 is moved (i.e. by a prime mover) relative tostator 20. The interaction of magnets 14 and the portions of the statorforming the primary magnetic circuit, creates a primary magnetic fluxwithin PM machine 10 along a primary magnetic flux path or magneticcircuit 60. The primary flux induces a voltage in the power winding 22which, when an electrical load is connected, results in an inducedcurrent and the induced current causes a secondary magnetic flux tocirculate an adjacent secondary magnetic flux path or magnetic circuit62. The primary circuit 60 and the secondary circuit 62 are thus coupledwhen a current flows in the power winding 22. The secondary magneticcircuit 62 is for the most part isolated from the rotor 12 and theprimary magnetic circuit 60. It is to be understood that thisdescription applies only to phase “1” of the 3-phase illustratedembodiment, and that similar interactions, etc. occur in respect of theother phases. Primary magnetic circuit 60 includes rotor 12, rotor airgap 34, power flux bus 36 and the portion of stator teeth 30 betweenrotor 12 and power flux bus 36. Primary magnetic circuit 60 encircles aportion of the power winding 22 and, in use as an alternator, causes acurrent flow in the power winding 22. Secondary magnetic circuit 62includes power flux bus 36, control bus 32 and the portion of statorteeth 30 between control bus 32 and power flux bus 36. In thisembodiment, the secondary magnetic circuit 62 encircles the portions ofthe power winding 22 and the control winding 24 in the second slotportion 28 b. The primary magnetic circuit 60 encircles the first slotportion 28 a while the secondary magnetic circuit 62 encircles thesecond slot portion 28 b. The first slot portion 28 a is preferablyradially closer to the rotor 12 than the second slot portion 28 b.

Power flux bus 36 is preferably common to both the primary and secondarymagnetic circuit paths, but need not be so. If desired, the power fluxbus 36 may be separated from the upper portion of the secondary fluxpath along the direction of flux lines so that the secondary magneticcircuit 62 be physically separated from the primary magnetic circuit(not shown).

A tertiary magnetic circuit 64 preferably circulates around control bus32, as partially indicated in FIG. 1 b (i.e. only a portion of thetertiary circuit is shown), as the tertiary circuit of the machine ofFIGS. 1 a to 1 c circulates through the entire stator 20, i.e. aroundits entire circumference. The control flux bus 32 is preferably commonto both the secondary and tertiary magnetic circuit paths and thus thesecondary and tertiary magnetic circuits are coupled. At least a portionof control flux bus 32 is saturable by the flux density of the tertiarymagnetic circuit. When operated as an alternator, the machine 10 permitsthe output of the power winding(s) 22 to be controlled through amanipulation of current supplied to the control winding(s) 24, as willnow be described.

As explained above, the equivalent power inductor 22′ is formed by theportion of the power winding 22 in the second slot portion 28 b and thesecondary magnetic circuit 62, as schematically represented by theequivalent circuit of FIG. 3. The control winding 24 shares thesecondary magnetic circuit 62, however since it is preferably wound inthe same direction around the control flux bus 32 in each second slotportion 28 b, as mentioned above, the resulting effect achieved issimilar to that provided by alternatingly reversed saturable inductors,and there is preferably substantially no net voltage generated withinthe control winding 24 by flux in the secondary magnetic circuit 62.

The application of a DC current from the source 50 to the controlwinding 24 results in a DC flux circulating circuit 64 in the controlflux bus 32. At the instant in time depicted in FIG. 1 b, it can be seenthat the DC flux in tertiary magnetic circuit 64 in the control flux bus32 is in the same direction in slot A as the AC flux in secondarymagnetic circuit 62, but in slot D the direction of the DC flux intertiary magnetic circuit 64 in the control flux bus 32 is opposite tothe AC flux in secondary magnetic circuit 62. As the DC current isincreased in the control winding 24, the flux density in the control bus32 is increased such that the saturation flux density is eventuallyreached. It will be understood that saturation is reached first in theregions in the control flux bus 32 where the AC flux and the DC flux arein the same direction, and that at higher DC control currents bothregions of the control flux bus 32 become saturated regardless of fluxdirection, if the current in the power phase winding is not sufficientto prevent saturation in the areas where the flux is in oppositedirections. If the current in the power windings is increased above thepoint where saturation of both regions is achieved, one of the regionswill come out of saturation. Once saturation occurs, the AC flux in thesecondary magnetic circuit 62 due to the current in the power winding 22is very significantly reduced.

As mentioned, the winding pattern of the control winding 24 relative tothe power winding 22 preferably results in a near net zero voltageinduced in the control winding 24, which simplifies control. Also, sincethe DC control current through the control flux bus 32 produces magneticfluxes in different directions relative to the power winding 22, oneportion of the control flux bus 32 will saturate more in one half cycleof the AC power while another portion of the control flux bus 32 willsaturate more in the other half cycle, thus tending to equalize thecontrol action through each half-cycle.

Once saturated, magnetic materials substantially lose their ability toconduct additional magnetic flux, and as such appear to be almostnon-magnetic to both AC magnetic forces (H_(AC)) and further changes inDC magnetic influence (H_(DC)). The net effect of this saturatedcondition in the control flux bus 32 is thus to virtually eliminate theinductance due to the secondary magnetic circuit 62, which therebysignificantly reduces inductance of the machine 10.

Furthermore, as the current flow in the power winding 22 increases, forexample due to an increase in the external load or an increase in thegenerated output voltage due to an increase in operating speed, theportion of the control flux bus 32 in which the flux directions areinstantaneously opposing will become less saturated, which causes aproportional increase in the inductance. This effect tends to cause theoutput current to remain somewhat constant. Thus the power outputcurrent of the alternator to become a function of the control current.The maximum inductance of the equivalent power inductor 22′ formed bythe secondary magnetic circuit 62 is related to the physical dimensionsand materials of the stator portions carrying the secondary magneticcircuit 62. The power winding current limit is related to the current inthe control winding by:I _(P) =K+[I _(C) *N _(C) /N _(P)]where: N_(P) and N_(C) are the number of turns in the power and controlwindings, respectively, I_(P) and I_(C) are the currents in the powerand control windings, respectively, and K is a constant which isinversely proportional to the maximum inductance of the power windingand other machine design features, as will be appreciated by the skilledreader.

This permits manipulation of the output of power winding 22, and thuscontrol winding 24 may be used as a source of control of PM machine 10.Means for controlling the operation of PM machine 10 are thus availablewithin the machine itself, as the “control” current may be generated bythe power windings 22 of the PM machine 10, typically in conjunctionwith rectifiers. In some instances, an external source of controlcurrent may be required or desired, in conjunction with an electroniccurrent control, although arranging the control winding 24 in serieswith the rectified output current may also be used to regulate outputvoltage to some extent. The architecture therefore lends itself to manynovel possibilities for control systems for the machine 10, a fewexamples of which will now described.

For example, the output (i.e. from a power winding 22) of alternator 10may be controlled by connecting the control winding 24 to a power supply50, and a current applied to the control winding 24 preferablysufficient to saturate the control flux bus 32 at a desired powerwinding current, such saturation being caused by magnetic flux flowingalong tertiary path 64 induced by current passing though control winding24, which is wrapped around control flux bus 32 in this embodiment. Whensaturation occurs, AC flux around the secondary magnetic circuit 62 iseffectively eliminated, and the magnetic relationship between the powerwinding 22 and the secondary magnetic circuit 62 is such that inductancedue to the secondary magnetic circuit in the power winding 22 isvirtually eliminated. Thus, more current is permitted to flow in thepower winding 22 than would flow without the saturating flux developedby the controlled DC current source. This increase in power windingcurrent will be limited at the point where the fluxes in opposingdirections become essentially equal in magnitude, resulting inde-saturation of the secondary magnetic circuit portions where this fluxequalisation condition occurs at that particular instant. Thede-saturation effect results in an abrupt increase in the inductance atthe instant corresponding to opposing flux equalisation, which in turnlimits the power winding current to the corresponding current value.Therefore, the current level provided by controlled current sourcesupply 50 can be continuously varied, as required, to regulate theoutput current of the power winding 22 (and thus, ultimately, outputvoltage) over a range of rotor speeds and electrical loads. In order toeffect constant output voltage control, for example, a feedback controlcircuit (discussed further below) is used by the control system ofsource 50 to compare the alternator output voltage (i.e. the output ofpower winding 22) to a fixed reference (e.g. representative of a desiredoutput voltage level(s)), and control can be configured such that, whenthe alternator output voltage is less than a desired reference level, acommand is provided to increase the control current to increasesaturation (thus de-saturation) level and therefore output current, andthus the output voltage across a given output load.

Magnetic flux preferably circulates the tertiary magnetic circuit 64 inthe same direction around the entire circumference of the machine 10,through the control flux bus 32. As mentioned above, although thecontrol winding 24 is provided in the second slots portion 28 bcorresponding to a particular phase of the three-phase machinedescribed, the power windings 22 are wound in the opposite direction ineach first slot portion 28 a which is due to the opposite polararrangement of the magnets 14 associated with each adjacent first slotportion 28 a of the phase. To ensure that a uniform direction for thetertiary magnetic circuit 64 is provided, as mentioned, the controlwindings 24 are preferably wound in the same direction in all secondslot portions 28 b. Also as mentioned, a net-zero voltage is induced inthe control winding 24, which is desirable because a relatively low DCpotential is then required to provide DC control currents, thus nospecial considerations are required to remove a significant AC potentialon the control winding 24.

Turning now to FIGS. 2 a, 2 b, 4 and 5, an improved multi-channel designof machine 10, of the general type described in applicant's U.S. Pat.No. 6,965,183 as modified in accordance with the present teachings, willnow be discussed.

Referring to FIGS. 2 a and 2 b, a 3-phase, dual “channel” machine isdepicted, and will now be described in more detail. The “dual channel”machine 10′ has two (in this embodiment) circumferentially distributed,distinct sectors with fully independent 3-phase sets of primary windings22 a, 22 b and associated secondary windings 24 a, 24 b are provided instator 20. Stator 20 is similar to the stator of FIGS. 1 a to 1 c, butis conceptually divided into two sectors 20 a and 20 b, denoted in FIG.2 a by the stippled line bisecting the stator. The separate winding sets22 a/22 b and 24 a/24 b of each channel, i.e. channels “A” and “B”, areconfined to these separate sectors 20 a, 20 b of the machine, whichthereby provides a “two-in-one” or dual-channel machine. Each of the twosets of 3-phase windings 22 a, 22 b is independently controllable andthus have the effect similar to as if two distinct machines wereprovided. As discussed in applicant's U.S. Pat. No. 6,965,183, thismulti-channel architecture permits a plurality of independentlycontrollable alternator sectors to exist within the same stator, andwhich may either be operated conjunctively or independently as desired.This feature thus permits more than one functional “machine” to existwithin the same stator structure.

As aforesaid, the electric machine 10 of FIGS. 2 a-2 b has a singlerotor 12 but two or more independent sectors in the stator 20, providingchannels A and B. These channels are independently controlled so that ifone has a failure, the other can continue its normal operation and mayperhaps be operated to compensate for the loss of the other. The outputof the channels, in normal operation, can be either combined to providea single output, or be used to supply different electrical devicesindependently, as desired. In a gas turbine application, this dual- ormulti-channel design permits a fully redundant system (system A+systemB, in FIG. 4) to be provided with a minimum of hardware, therebyminimizing weight and space and increasing reliability. Among otherthings, this offers inherent redundancy useful in aerospaceapplications. As well, since generator efficiency is inverselyproportional to I²R losses, it is often preferable to run two machines,each at ½ of the output current, rather than one machine a full outputcurrent.

As discussed with respect to the machine in FIGS. 1 a-1 c, the tertiarymagnetic circuit of that machine encircles the entire circumference ofthe stator, however in the multi-channel design of FIGS. 2 a-2 b, thereis not the case. Referring to FIG. 2 b, since control windings 24 a and24 b are independent, and respectively interact with independentwindings 22 a and 22 b, separate tertiary magnetic circuits 64 a and 64b result in dual-channel machine 10. The tertiary magnetic circuits 64a/64 b instead travel along the entire length of the control flux bus 32to the channel boundary (indicated by the stippled line in FIG. 2 a),where it then tends to turn up to the power flux bus 36, where it thentravels back along entire length of the power flux bus 36 until the pathjoins up again with the beginning of the tertiary magnetic circuits 64a, 64 b, as the case may be. For clarity, the primary and secondarymagnetic circuits are not indicated in FIG. 2 b. At the boundary betweenchannels, however, there is a potential for flux leakage, or“crosstalk”, between the magnetic flux circulating tertiary magneticcircuits 64 a and 64 b.

To reduce the occurrence of such crosstalk, a stator features orfeatures such as a slit 70 is provided in the control bus 32 betweeneach channel of the machine 10. Since the illustrated embodiment has twosections A, B, two slits 70 are provided. The slits 70 can be made bymachining, using for instance a cutoff saw or wire EDM. If desired, eachslit 70 may be filled with a solid non-magnetic material, which willhelp seal the area when a coolant fluid is circulated in the machine 10,or may be filled with a magnetic material but of preferably much lowermagnetic permeability. The slits 70 can also be formed during thelamination stamping process.

In use, when slits 70 are provided, the flux circulating tertiarymagnetic circuits 64 a and 64 b can be electromagnetically separatedmore effectively, and thus allow the channels to be operated moreindependently, since the slits 70 substantially impede the transfer ofmagnetic flux across the limit between the channels. Without the slits70, the magnetic flux tends to stray somewhat into adjacent channels ofthe machine 10, given that the control bus 32 is made of a highlypermeable magnetic material. This crosstalk can interfere with theindependent control may reduce the ability of optimally controlling onesection if the other has a fault, or vice versa. The presence of across-talk reduction feature, such as stator slit 70, acts tosubstantially contain the tertiary magnetic within the channel. Wheremore than two channels are provided, preferably at least cross-talkreduction feature is provided at each boundary. Although the cross-talkreduction features need not be exactly co-located with each boundary, itis generally preferred that they are.

The cross-talk reduction feature(s), such as slit 70, is preferablydesigned to effectively limit crosstalk between channels to the extentrequired to meet the design objectives. The design, shape, size andconstruction of such feature will depend in large part on the machinedesign and operating parameters. Here, for example, the slits 70 willpreferably have a width and depth required to meet the disclosedobjectives. In this design, the radial depth of slits 70 extend to aradius or level about even with the bottom of second slot portions 28 b.

FIG. 5 shows an exploded view of the stator power windings 22 a, 22 b ofthe dual-channel three-phase electric machine of FIGS. 2 a and 2 b, andthe control slit 70.

The above description is therefore meant to be exemplary only, and oneskilled in the art will recognize that other changes may also be made tothe embodiments described without departing from the scope of theinvention disclosed as defined by the appended claims. For instance, thepresent invention is not limited for use with a dual-channel machine asmachines can have more than two channels in some designs. The windingsmay have single or multiple turns per slot, the number of turns of awinding not necessarily has to be a whole number. The number of powerwindings does not necessarily have to equal the number of controlwindings, and one or more windings may perhaps be present in a slot. Thewindings may be any conductor(s) (i.e. single conductor, more than onewire, insulated, laminated, Litz etc.) or may be superconductors. Inmultiphase machines, there may be delta or Y-connected windings inaccordance with known techniques. There need not be an air gap betweenthe power and control windings, as long as the windings are electricallyisolated from one another. The rotor can be any electromagneticconfiguration suitable (i.e. permanent magnet rotor not necessary), andmay be provided in an outside or inside configuration, or any othersuitable configuration. Other winding configurations are possible, andthe ones described above need not be used at all, or throughout theapparatus. Also, the magnetic circuits described can be arranged in thestator (and/or rotor) in any suitable manner. Likewise, the stator androtor may also have any suitable configuration. Any suitable saturationmeans may be used. Although a DC source is preferred for control ofsaturation in some embodiments described above, an AC source may also beused in certain circumstances to achieve desired results, as the skilledreader will understand. Still other modifications which fall within thescope of the present invention will be apparent to those skilled in theart, in light of a review of this disclosure, and such modifications areintended to fall within the appended claims.

1. An electric alternator/motor comprising: a rotor having a pluralityof permanent magnets; a stator having at least two non-overlappingsectors, each sector having a plurality of first slots and a pluralityof second slots, the first slots being located on a periphery of thestator opposing the rotor, the second slots being located on an oppositeside of the first slots relative to the rotor, at least a first windingdisposed in a plurality of said first and second slots, at least a firstmagnetic circuit which encircles at least one first slot in which aportion the first winding is disposed, at least a second magneticcircuit encircling at least one of the second slots in which anotherportion of the first winding is disposed, the second magnetic circuitremote from the first magnetic circuit, at least a second windingdisposed adjacent to the first winding in the plurality of second slots,a third magnetic circuit defined in the stator, the third magneticcircuit operatively associated with current passing through the secondwinding, and a current source connected to the second winding andadapted to pass current through the second winding to thereby causemagnetic flux to circulate third magnetic circuit; and at least one slitbetween each sector of the stator adjacent to the respective thirdmagnetic circuits, each slit separating the third magnetic circuits ofadjacent sectors and thereby adapted to impede magnetic flux crossingbetween the third magnetic circuit of each sector.
 2. The electricalternator/motor of claim 1, wherein there are two sectors and twoslits, the sectors of equal size and the slits diametrically opposed onthe stator.
 3. The electric alternator/motor of claim 1, wherein theslits are defined in a periphery of the stator.
 4. The electricalternator/motor of claim 1, wherein the slits extend radially into thestator to a depth substantially aligned with a periphery of the secondslots.
 5. The electric alternator/motor of claim 1, wherein each slit isfilled with a material having a lower magnetic permeability than thesurrounding stator material in which the slit is provided.
 6. Theelectric alternator/motor of claim 1, wherein each slit is filled with asolid non-magnetic material.
 7. A machine operable as at least one of anelectric alternator/generator and an electric motor, the machinecomprising a rotor and stator assembly, the assembly having a statorwith at least two non-overlapping sectors, each sector including atleast a first winding, first and second magnetic circuits and asaturation control assembly, the first magnetic circuit including therotor and encircling at least a first portion of the first winding, thesecond magnetic circuit encircling at least a second portion of thefirst winding remote from the first magnetic circuit, the first andsecond magnetic circuits coupled when current flows in the firstwinding, the saturation control assembly of each sector beingoperatively associated with the corresponding second circuit andoperable to controllably vary a saturation level of a portion of itsassociated second magnetic circuit, the saturation control assemblyhaving a third magnetic circuit associated therewith which travels alonga periphery of the stator, the respective third magnetic circuits of thesectors being electromagnetically separated by at least one slit in saidperiphery of the stator.
 8. The machine of claim 7, wherein thesaturation control assembly includes at least a second winding and avariable output current source connected to the second winding, currentin the second winding resulting in magnetic flux circulating the thirdmagnetic circuit, wherein the second winding is provided in the statorsuch that when a current level in the second winding is varied, thesaturation level of said saturable portion is varied.
 9. The machine ofclaim 7, wherein there are two sectors and two slits, the sectors beingof equal size and the slits being diametrically opposed on the stator.10. The machine of claim 7, wherein the slits extend radially into thestator to a depth substantially aligned with a periphery of the secondslots.
 11. The machine of claim 7, wherein each slit is filled with amaterial having a lower magnetic permeability than the surroundingstator material in which the slit is provided.